Theodolite



(No Model.) 2 Sheets-Sheet 1.

T. H. BERGH 6.4.. M. JOHNSON. THEODOLITE.

No. 543,122." Patented July 23, 1895..

K Ar.

(No Model.) .2 Sheets-Sheet 2.

T. H. BERGH 8a A. M. JOHNSON;

THEQDOLITE.

Nb. 543,122. Patented July 23, 1895.

MOO M g mmiwm;

UNITED STATES PATENT OFFICE.

MINNESOTA.

TH EOD OLlTE.

SPECIFICATION forming part of Letters Patent No. 543,122, dated J uly23, 1895. Application filed January 1895. Serial No. 536,201. (Nomodel.) I

declare the following to be a full, clear, and

exact description of the invention, such as will enable others skilledin the art to which it appertains to make and use the same.

Our invention relates to theodolites, and has for. its object to provideacheap and efficient instrument of the above class.

To these ends our invention comprises the novel devices and combinationsof devices, the

preferred form of which, as well as a modification of the same, areillustrated in the accompanying drawings, wherein like letters refer tolike parts throughout the several Views.

' In the preferred form of our device we employ one or moresighting-tubes, each of which have open outer ends, and at their innerends small sight-openings located centrally of said tubes andcooperating with said open ends to give the diverging sighting-lines.The pivot points of the sighting-tubes must. be eccentric to or offsetfrom the focal point of the sighting-lines to give a base to the-angleof measurement, as will appear later on.

' Referring to the drawings, Figure l is a plan view of the preferredform of our device. Figs. 2 and 3 are respectively a side elevation anda front elevation of the same, some parts being broken away. Fig. 4is aview in plan representing, in diagram, the sighting lines andcross-sections of the sighting-tubes employed in said preferred form;and Fig. 5 is a similar view to Fig. 4 showing a simplified modificationof the device, illustrating the manner of measuring distances with asingle sighting-tube.

a b are a pair of sighting-tubes having open outer ends and thesight-openings a b, respectively, at. their inner ends. Of these tubesthe one a is held in its properly-adj usted position by means of arigidly-secured pivot-stem on working through a bearing 0 of a tripod orstandard 0' and subject to a thumbscrew 0 The tube b is pivoted to theforward end of the tube aby means of a depending tube-like support bfixed to said tube 1) and working around a stud a projecting from saidtube a. Thus the tubes a and b are both mounted for pivotal adjustmentin horizontal planes. The tube a has secured thereto and projectingtherefrom a segmental scale a, which is marked to indicate the distancesmeasured by the different angular positions of the two tubes a and?)with respect to each other, and the stem b of the tube 1) carries apointer 19 which co-operates with said segmental scale to indicate thisadjustment.

The outer open ends of the tubes at and b are preferably provided withcross-wires 0. b, respectively, which serve to clearly mark thediainetrical opposite points of said tubes both with respect tohorizontal and vertical planes. The use of the single tube a is shown inFig. 5.

' It is thought that it will facilitate the ready understanding of theprinciples of construction of our invention by considering first the useof the single tube illustrated in Fig. 5, which is as follows: Let 25represent, for instance, the bank of a distant river, the distance ofwhich from the instrument is to be determined. Now let the observer,looking through the sight-hole a, sight an object on the bank 25 whichfalls on the visual line 00, as marked at 00. Then let the observer,looking on the visual line yagainst the opposite side of the open end ofthe tube, turn said tube until this visual line y is directed onto theobject 00'. Now, as is evident, the farther this object m is from theinstrument the less will be the necessary angular movement of thesighting-tube to bring successively the visual lines a: and y in linethereon, and conversely, the nearer this object 00 the greater will bethis angular movement of the tube. To illustrate, suppose the object tobe at a point on the line as, represented at As is obvious, it wouldtake a farther angular movement of said tube a to bringthe visual line yin line therewith.

In case the single tube a alone is used, as indicated above, the samemay be provided with a pointer p and be pivoted to'a relatively-fixedbracket 19, which terminates in a scale 19 co-operating with saidpointer 13 to indicate the angular movement of said tube a.

From the foregoing it must be evident that with a single tube, bycalculating the angular movement through which the tube is moved in theabove-described operation, the distance of objects from the observer maybe determined; but this device is subject to an objection, which arisesfrom the fact that it is extremely dillicult to keep from losing anobject which is first sighted by one of the visual lines of the tubewhile the tube is being adjusted to throw the other visual line on saidobject. Especially is this so in sighting dis taut objects, such as amountain, which may present no distinct marks upon which to direct thesight. This objection is removed in the preferred form of my device,wherein two sighting-tubes are employed. The operation of this preferredform is very similar to that described in Fig. 5, and the essentialdifferences may be briefly stated, as follows: The observer, lookingthrough the opening a of the tube a, sights the object 00 on the lineat, and the tube a is fixed in this position. Then the observer, lookingthrough the sight-opening Z) of the tube Z) on the visual line 2, turnssaid tube 1) until the visual line .2 is directed onto the object on.With this arrangement, as is evident, the observer, after having oncesighted an object or a particular point on an object, need not losesight of the same while adjusting the second tube into its propersighting position thereon. It will be further noted that the visualangle or cone of vision of the tubes a and b are greater one than theother. In view of this fact, as is evident by reference to Fig. 4,distances may be measured in several different waysas, for example, bybringing the visual line y of the tube a and the visual line .2 of thetube 1) to a focus on the object; or, again, by bringing one of the sidelines of the cone of vision of either one of the tubes and the centralline of vision of the other tube to a focus on said object. The centralline of vision of the tubes is indicated by the line marked to.

As the constant angle of the cone of vision of any particularsighting-tube is known, it follows that the diametrical dimensions ofsaid cone at all distances are determinate; and hence, after thedistance of an object is determined, the transverse distance of thelandscape orobjeet surveyed, looking through said tube, can therefore bedetermined.

It will be readily understood that various alterations in the details ofconstruction of our device may be made without departing from the spiritof our invention.

hat we claim, and desire to secure by Let ters Patent of the UnitedStates, is as follows:

1. In a theodolite, the combination with a suitable support, of thesighting-tube, pivoted thereto, having an open .outer end, and thecentrally located sight-hole at its inner end, cooperating with saidopen outer end to give a predetermined cone of vision, substantially as,and for the purposes set forth.

2. In a theodolite, a pair of sighting-tubes pivoted one upon the other,each of said tubes having open outer ends, centrally located sight-holesat their inner ends, which sightholes cooperate with the open ends oftheir respective tubes, to givepredeterminedcones of vision, and anindicating device for measuring the angle of rotation of said tubessubstantially as, and for the purpose set forth.

3. In a theodolite, the combination with a pair of sighting-tubespivoted one upon the other, each of said tubes having open outer ends,and centrally located sight-holes at their inner ends, which sight-holescooperate with the open ends of their respective tubes, to givepredetermined cones of vision, of an indicator-scale and pointer,carried one with each of said tubes, said scale being marked withnotations which denote distances represented by different angularadjustments, substantially as described.

In testimony whereof we affix our signatures in presence of twowitnesses.

THORWAL'D H. BERGII.

ANDREW M. JOHNSON.

Vitnessesz- JAS. F. WILLIAMsoN, E. F. Emuonn.

